The present embodiments relate to identifying forces in an interface between a body and a suspension of a vehicle. In particular, an arrangement of sensors and modeling are used to estimate forces.
In order to reduce fuel consumption, car manufacturers develop lighter, and hence more flexible, body structures. Modifications to the car body have an influence on vehicle dynamics performance. Nevertheless, there are still many unknowns. In order to design lighter car bodies while maintaining similar vehicle dynamics performance, car manufacturers look to forces acting in the interface between the suspension and the body for insight. These forces cannot be measured directly using transducers without altering the interface, so instead the forces are estimated.
To estimate the forces, strain gauges are mounted on the body of the car as close as possible to the connection points with the suspension. To obtain reliable results, the number of strain gauges to be instrumented equals at least three times the number of forces to be identified, such as having more than 200 strain gauges. A skilled technician may install approximately ten gauges a day, taking one technician around 20 days to instrument a car with strain gauges. Once installed, deformations are measured by the strain gauges in response to a controlled application of force, such as an impact hammer on the car body in a trimmed-body condition (i.e., without the suspension). Transfer functions from the force inputs to the strain responses are computed and assembled in a frequency-response-function (FRF) matrix, which is inverted. The suspension is added to the car body and handling maneuvers are performed on a test-track while strain data is measured. With the measured operational strain data and the inverted FRF matrix, the time-domain forces acting in the body-to-suspension interface are estimated. However, this approach results in high costs and a time frame that may not fit in the development cycle of the car.